1. Technical Field
The present invention relates to an organic semiconductor film and an organic semiconductor device having the organic semiconductor film.
2. Related Art
Examples of semiconductor devices include thin film transistors (TFT) that have been put to practical use as switching elements in an active matrix liquid crystal display, for instance, and designed to use an amorphous or polycrystalline silicon semiconductor film.
As TFT semiconductor materials, organic semiconductor materials have drawn attention in recent years. Organic semiconductors can be easily processed into a thin film by a simple deposition method such as spin coating and vacuum deposition, and processed at lower temperatures than conventional TFT using amorphous or polycrystalline silicon. Lower processing temperatures permit the forming on a plastic substrate with low thermal resistance, and thereby having various expected effects including reduction in display weight and manufacturing cost and versatile applications utilizing the flexibility of a plastic substrate.
In developing TFT using conventional organic semiconductor materials, however, it is difficult to control the threshold voltage and channel conductivity by impurity doping, which is performed for TFT using amorphous or polycrystalline silicon. This has been one of the factors preventing its practical use. A technology reported by Jiyoul Lee et al (e.g. Applied Physics Letters, Vol. 80: 2925-27, 2002) relates to threshold voltage, but it is not intended to arbitrarily control threshold voltage.
As for the control of channel conductivity, it is necessary to select appropriate organic semiconductor materials to manufacture n-channel or p-channel thin film transistors.
A complementary metal-oxide semiconductor (CMOS) transistor which consists of an n-channel MOS (nMOS) transistor and a p-channel MOS (pMOS) transistor that are combined in an IC chip is widely known as a semiconductor device. The CMOS transistor has a basic structure in which enhancement-mode nMOS and PMOS transistors are coupled in series and has n-channel and p-channel regions.
However, impurity cannot be doped into an organic semiconductor material for producing the CMOS transistor. Therefore, it is necessary to produce semiconductor films for the n-channel and p-channel regions separately, which complicates the manufacturing process and reduce productivity.
In consideration of the above-described problem, the present invention aims to provide an organic semiconductor film and organic semiconductor device that are capable of producing n-channel and/or p-channel regions without changing materials for forming organic semiconductor thin films in particular, and also capable of controlling threshold voltage.